Hormones play a vital role in the regulation of cellular activity. An understanding of the initial event of hormone action, the interaction of hormone with its receptor, is necessary for designing antagonists and superactive agonists useful in therapy of endocrinological disorders. We propose to study the pheromone a-factor (YIIKGVFWDPAC[FARNESYL]-OCH3) as a model for lipopeptide structure and function. Farnesylation of proteins is a newly-discovered, post-translational modification that has been shown to play a critical role in directing modified peptides and proteins to the plasma membrane. Examples of eukaryotic proteins that contain the post-translational polyisoprenoid modification include nuclear lamins, trimeric G proteins, and the RAS family of oncoproteins. Thus, the study of the interaction of a-factor with its receptor and target cell should provide novel information to elucidate the molecular events involved between lipopeptides and cells. We propose to use a combined approach of chemical synthesis and oligonucleotide-directed, random mutagenesis to discover antagonists and superactive agonists. By developing an assay to study the interaction of a-factor and a-factor analogs with its receptor we hope to delineate those residues and molecular groupings involved in pheromone binding. By studying and cloning a newly discovered a-factor protease we hope to uncover the role of lipopeptide degradation in desensitization and recovery of the target cell from pheromone action. By determining whether and how a-factor is internalized we hope to elucidate the cellular fate of hydrophobic molecules subsequent to cellular binding. We believe that the system we propose to investigate will be useful for drug screening for the discovery of important new pharmacological reagents to treat a variety of human diseases.